As is known, electromagnetic (EM) radiation can have a non-zero orbital angular momentum (OAM), and EM beams (e.g., radio frequency beams) with a non-zero OAM can be transmitted and received. FIG. 1A illustrates a simplified, block diagram depiction of an OAM EM beam 102. As shown, the OAM EM beam 102 turns (i.e., twists) about an axis 104 in the direction of propagation of the beam 102. For example, the wave front of the beam 102 can be substantially spiral or helical. The numerical value of the mode m of the beam 102 corresponds to the time or distance (labeled 106 in FIG. 1A) between one full revolution of the beam 102 about the axis 104, and the sign of the mode m corresponds to the direction (e.g., right or left) of the revolutions of the beam 102 about the axis 104.
Multiple OAM beams (each generally similar to beam 102) each in the same frequency band but having a different mode m can be combined and transmitted as a combined transmission from an EM transmitter (not shown). An EM receiver (not shown) can received the combined transmission and separate the multiple OAM beams. The ability to combine multiple beams in the same frequency band provides for the possibility of very high data rate transmissions.
FIG. 1B illustrates an example of a far field pattern 110 of the EM field intensity of a typical OAM beam 102 in a plane that is perpendicular to the direction of propagation (i.e., perpendicular to the axis 104). As shown, much of the far field pattern 110, including a central region 114 around the axis 104 of propagation, has a low EM field intensity. High intensity EM fields tend to be in a ring (corresponding to 112 in FIG. 1B) around the central region 114.
As is known, an EM beam tends to spread out as it propagates. The far field pattern 110 is thus typically much larger than a distant receiving antenna (not shown). It can be difficult, however, to point a transmitting antenna (not shown) at a receiving antenna (not shown) because the high intensity region 112 is not concentrated at the center of the beam 102. Moreover, because the far field pattern 110 in a point-to-point link is typically so much larger than the receiving antenna (not shown), energy in the transmitted beam 102 that is anywhere other than the typically small portion of the far field pattern 110 at which the receiving antenna (not shown) is located is wasted. Some embodiments of the present invention address one or more of the foregoing issues with the prior art and/or provide other advancements and advantages.